It is enabled by entering Mode 13h via an BIOS system call, then changing the values of several VGA registers.
[3][4] Planar memory arrangement splits the pixels horizontally into groups of four.
For any given byte in video memory, four pixels on screen can be accessed depending on which plane(s) are enabled.
This is more complicated for the programmer, but the advantages gained by this arrangement—primarily the ability to use all 256 KB of VGA memory for one or more display buffers, instead of only one quarter of that (64 KB)—were considered worthwhile by many.
[5][6] The Y coordinate can simply be put in the high byte of the address, and the X coordinate in the low byte, forming the address of the pixel without a multiply.